Currently, nREPL's interruptible-eval middleware hardcodes a dependency on pr-values. It would be nicer if the user could either specify alternate rendering middleware or if nREPL's built-in middleware accepted an arbitrary function to render values with. Specifically, this would enable pretty-printing REPL output.

Currently it is possible to replace the default middleware, but it involves some ugly runtime metadata manipulation which reaches into the nREPL internals. Addressing this would be another step towards simplifying pretty-printing/color integration in the REPL.